﻿#region Copyright and Licensing Notice
// Copyright (C) 2011 Steven Bosnick
// 
// This program is open source software; you can redistribute it 
// and/or modifiy it under the terms of the Eclipse Public License,
// version 1.0.
// 
// This program is distributed in the hope that it will be useful, 
// but WITHOUT ANY WARRANTY; without even the implied
// warranty of MERCHANTABILITY or FITNESS FOR A 
// PARTICULAR PURPOSE. See the Eclipse Public License for more
// details.
// 
// You should have received a copy of the Eclipse Public License 
// along with this program; if not, you can find a copy at
// "http://www.opensource.org/licenses/eclipse-1.0.php".
#endregion
using System;
using BitwiseOre.SharedMemory.JetBrains;

namespace BitwiseOre.SharedMemory.Core.Primatives
{
    [UsedImplicitly]
    internal sealed class GuidQueueSizer : IGuidQueueSizer
    {
        private const int VirtualMemoryFactor = 4;
        private readonly IMemoryStatus _memoryStatus;

        public GuidQueueSizer(IMemoryStatus memoryStatus)
        {
            _memoryStatus = memoryStatus;
        }

        public long Size(int count)
        {
            return checked(QueueConstants.GuidQueueFixedSize + ((long)count)*QueueConstants.GuidQueueVariableSize);
        }

        public bool IsCountTooLarge(int count)
        {
            return count > int.MaxValue/QueueConstants.GuidQueueElementSize
                   || (ulong) Size(count) > _memoryStatus.GetAvailableVirtualMemory()/VirtualMemoryFactor;
        }

        public int GetCurrentMaximumCount()
        {
            checked
            {
                const int count1 = QueueConstants.MaxQueueIndex;
                var memory = (long) (_memoryStatus.GetAvailableVirtualMemory()/VirtualMemoryFactor);
                var count2 = (memory - QueueConstants.GuidQueueFixedSize)/QueueConstants.GuidQueueVariableSize;

                return Math.Min(count1, (int)count2);
            }
        }
    }
}